Oil spills are extreme environmental perturbations (i.e. ecological catastrophes) affecting marine food webs and especially top predators, in which effects are likely amplified. As such, seabirds suffer from direct mortality and food depletion, with potentially important consequences for the population growth rate and probability of extinction. However, little is known about the effects of sex-skewed mortality (due to sex spatio-temporal differences in at-sea distribution) in seabird population dynamics. We analyzed the mortality of European shags Phalacrocorax aristotelis after the Prestige oil spill and its effects on breeding colonies in Galicia (southwest North Atlantic). Most adults found dead were females (85%). The year after the spill, Monte Carlo simulations of population trajectories predicted a reduction of 11% in the number of breeding pairs when skewed mortality was considered, and a lower rate (8%) when assuming random sex distribution of adult mortality. The further reduction predicted with the sex-biased mortality was probably the result of unmated adults unable to reproduce. This difference, although slight, is a concern for conservation owing that the colonies studied were already showing a 5% annual decline due to other factors also related to human activities.
Dietary studies of seabirds provide information on food webs and oceanographic variability. Studying fatty acid signatures (FAS), which reflect changes in the composition of the diet, has several advantages over traditional methods. In the context of the Mediterranean marine ecosystem, we studied tissue FAS in captive-fed and wild seabirds. Yellow-legged gulls Larus michahellis were experimentally fed either pelagic (sardine Sardina pilchardus) or demersal (spotted flounder Citharus linguatula) fish for 8 wk, and FAS in the birds' plasma and adipose tissue were studied. The FAS developed patterns characteristic of the sardine or flounder diet, showing the reliability of both types of samples. In addition, plasma samples of 20 endangered wild Balearic shearwaters Puffinus mauretanicus and their most likely prey items from the Mediterranean Sea were collected and analyzed for FAS. Based on FAS of Mediterranean fish, and the results from the feeding experiment, the diet of the endangered wild shearwaters was estimated. In terms of the composition of polyunsaturated fatty acids, the plasma FAS of the shearwaters resembled those of the captive gulls kept on a sardine diet, suggesting that pelagic feeding resources dominate shearwater diet. However, the high level of 20:1n-11, likely metabolized from 22:1n-11 by the birds themselves, suggested that the diet also contained a demersal component rich in 22:1n-11. Contrary to the situation in the open oceans, the levels of the C20 and C22 monounsaturated fatty acids are low in the Mediterranean food web and characteristic of most demersal species. Our results support the findings of previous field studies that the diet of the shearwaters is frequently supplemented by demersal fish from fishery discards.
: Reintroduction of captive‐reared animals has become increasingly popular in recent decades as a conservation technique, but little is known of how demographic factors affect the success of reintroductions. We believe whether the increase in population persistence associated with reintroduction is sufficient to warrant the cost of rearing and relocating individuals should be considered as well. We examined the trade‐off between population persistence and financial cost of a reintroduction program for Crested Coots (Fulica cristata). This species was nearly extirpated from southern Europe due to unsustainable levels of hunting and reduction in amount and quality of habitat. We used a stochastic, stage‐based, single‐sex, metapopulation model with site‐specific parameters to examine the demographic effects of releasing juveniles or adults in each population for a range of durations. We parameterized the model with data from an unsuccessful reintroduction program in which juvenile captive‐bred Crested Coots were released between 2000 and 2009. Using economic data from the captive‐breeding program, we also determined whether the strategy that maximized abundance coincided with the least expensive strategy. Releasing adults resulted in slightly larger final abundance than the release of nonreproductive juveniles. Both strategies were equally poor in achieving a viable metapopulation, but releasing adults was 2–4 times more expensive than releasing juveniles. To obtain a metapopulation that would be viable for 30 years, fecundity in the wild would need to increase to the values observed in captivity and juvenile survival would need to increase to almost unity. We suggest that the most likely way to increase these vital rates is by increasing habitat quality at release sites.
SUMMARYA conservation project aimed at ecosystem restoration had several unforeseen effects on a colony of the yellow-legged gull Larus michahellis in a small western Mediterranean island (Benidorm Island). The project included regulation of massive tourist visits to help restore the soil and autochthonous vegetation. However, gulls habituated rapidly to regulation of tourist activities, as nests located either close to or far from the main trail showed a similar hatching success. The quiet conditions produced by regulation seemingly facilitated a rapid colony increase. Partial removal of alien vegetation (Opuntia maxima) showed that gulls had a preference for sites with high vegetation cover because the growth of the colony was proportionally larger in well-vegetated plots. The pricking of a large number of gull eggs surprisingly coincided with a high reproductive success compared to the previous year, although indicators of food availability remained constant between years and the colony had decreased in numbers. Untreated nests were probably more successful because territory size for chicks increased and intraspecific predation decreased. Extreme care must be taken when planning ecosystemwide management on islands with yellow-legged gull colonies, or other gull species locally considered as pests, to prevent unwanted effects.
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